1. Field of the Invention
The invention relates to a welded vehicle wheel having a sectional rim which is connected to a nave or wheel disk in the area of the drop center by means of a weld seam,
2. Discussion of the Prior Art
In the course of the standardization of goods and products in the European market, certain sections have also been uniformly defined for the rims of vehicle wheels. This applies in particular to the rim flanges and the bead seat area in terms of their axial and/or radial extent, transition radii and angles. However, there are also sections, in particular in the drop center area, whose design can to a certain extent be freely determined by the manufacturer of the rim.
If, in the first instance, the wheel is considered under load, it is similar, viewed in elastic terms, to a flattened egg because the wheel is deformed by the weight of the vehicle and is pressed flat with the underlying surface in the vicinity of the contact area. The rotation of the wheel causes the egg shape to migrate around the wheel with the result that respective alternating stresses occur. A critical area in this respect is the weld point of the nave and/or of the wheel disk in the drop center area. Here, when the wheel is subject to severe loading, fractures may, under certain circumstances, occur. The weld point is also problematic in that the application of the welding heat causes the cold-hardened structure of the rim to become recrystallized and coarse-grained.
PA J (Patent Abstracts of Japan) 07223402 A discloses a vehicle wheel which has a sectional rim which is connected to a wheel disk in the area of the drop center by means of a weld seam. In contrast to usual conventional sectional rims, the rim has a section of the drop center which has a pronounced radially thickened portion on the outside of the wheel. This thickened section is provided on the inside at the outer end with a right-angled shoulder against which a projection, arranged on the outermost circumference, on the wheel disk comes to bear when pressing-in occurs. Such a thickening of a rim section increases the rigidity of the vehicle wheel but is unfavorable in terms of the weight and the formation of faults in the area where material accumulates. The faults in turn cause an unbalance of the vehicle wheel.
A different type of structure is disclosed in German reference DE 33 11 697 A1. The sectional rim which is provided with a drop center has a double or even triple hump on the outside of the wheel, the hump which lies axially further toward the inside being smaller in diameter than the hump which lies further toward the outside. The respective hump extends continuously over the circumference and is located in a plane at right angles to the axis of the rim. The center point of the respective hump is eccentric to the axis of the rim. The eccentric position of the humps in different axial positions leads to a dynamic unbalance and causes the vehicle wheel to undergo oscillations which cannot be overcome at all or can be overcome only partially by applying compensation weights.
A passenger car wheel of a particular design is presented in German reference DE 37 04 384 A1. The sectional rim which is manufactured from sheet metal has a drop center which is provided with a cambered part which extends radially outward. A nave which is produced from sheet metal and which is provided in the annular circumferential part with a bead which fits the cambered part in a complementary fashion can be clipped into this cambered part. This cambered part in the drop center of the rim does not provide reinforcing but rather serves only to hold the nave which can be clipped in.
The object of the invention is to modify a welded vehicle wheel of the generic type in such a way that, without increasing the weight, the risk of fracturing in the area of the weld point is minimized, even when the wheel is subjected to severe loading. which reinforces the rim and extends radially and over the entire circumference. The center axis of the cambered part is coaxial with the axis of the rim and is located outside the usual rim section. Preferably, the cambered part is located in the area of the drop center and/or ledge. This selective reinforcement can be used to reduce the previously necessary minimum thickness for the rim. However, at the same time, it is necessary to bear in mind that a portion of the resulting reduction in weight is used up again by the greater length of the rim when stretched out, which results from the cambering, and in the worst case is cancelled out by it. However, because the reduction in weight is not the main object of the invention, but rather a welcome secondary effect, the vehicle wheel according to the invention fulfills the more important requirement relating to the loading of the critical area of the weld point, even when the weight is unchanged.